The present invention relates to apparatus for making perforations in flexible webs, sheets, strips, tapes or like materials, for example, in wrapping materials for fillers consisting of natural, substitute and/or reconstituted tobacco or of filter materials. More particularly, the invention relates to improvements in apparatus for making perforations in running webs, strips or like bodies (hereinafter called webs for short) of flexible sheet or foil material, preferably a material which is used in the tobacco processing industries to constitute wrappers for tobacco, filter material or both. Still more particularly, the invention relates to improvements in apparatus for making perforations by resort to devices for directing radiant or other energy against selected portions of a running web so as to provide therein one or more annuli, rows or files of perforations in the form of round and/or otherwise configurated holes.
It is known to provide the wrappers of smokers' products, such as plain or filter tipped cigarettes, cigars or cigarillos, with perforations which serve to admit atmospheric air into the column of tobacco smoke. The relatively cool atmospheric air is believed to beneficially influence the quantity of nicotine and condensate in the tobacco smoke. For example, if the smokers' products are filter cigarettes, the perforations are normally provided in that portion of the tubular envelope of the filter plug which is adjacent to the tobacco-containing portion of the cigarette. The perforations can be made in the wrapping material prior to draping around tobacco fillers and/or filter material, or in the tubular envelopes of finished smokers' products.
In accordance with a known proposal, the source of energy is a laser which is installed and whose beam is deflected and/or otherwise influenced in a manner as disclosed, for example, in German Offenlegungsschrift No. 2,754,104. It has been found that coherent radiation which is emitted by a laser can provide a sheet-like material with zones of highly predictable permeability irrespective of whether the perforations are made in the wrappers of finished or semifinished smokers' products or in the running web or webs which are thereupon converted into wrappers of plain or filter cigarettes or the like.
Another known mode of making perforations in the envelopes or wrappers of rod-shaped smokers' products is by resort to an electroperforating apparatus wherein the web is guided through one or more gaps defined by one or more pairs of electrodes having different polarities. The electrodes are connected to an energy source which causes sparks to jump across the gaps between the pairs of associated electrodes with the resultant formation of perforations in those web portions which happen to be located in the gap or gaps. Reference may be had to commonly owned German Offenlegungsschrift No. 2,934,044.
A drawback of the above described conventional perforating apparatus is that solid combustion products which develop as a result of making perforations in a web of paper, cardboard, imitation cork or the like are likely to interfere with the operation of such apparatus, and more particularly to prevent the making of perforations having a predictable size and/or shape so that the permeability of the ultimate product deviates from an optimum permeability. As a rule, the combustion products (this term is intended to embrace fully combusted solid remnants of the material which is removed to make perforations as well as partially combusted fragments of foil, cardboard, paper or the like) will float around the perforating station or stations and will tend to deposit at the outlet or outlets of the device or devices which discharge beams of coherent radiation or on the electrodes of an electroperforating apparatus. Commonly owned copending German patent application Ser. No. P 31 14 603.1 discloses a perforating apparatus which is designed to maintain the solid combustion products away from the locus of impingement of beams of coherent radiation upon a running web of cigarette paper or the like. This is achieved by providing means for directing streams of air through the radiation directing device or devices so as to ensure that any particles which are removed from the running web as a result of impingement of one or more beams of coherent radiation will be blown away from the radiation-directing means as well as away from the perforating station or stations proper, i.e., away from the locus or loci of impingement of coherent radiation upon the running web. If the web is perforated during travel through one or more gaps between one or more pairs of electrodes, the apparatus can be equipped with means for establishing and maintaining streams of air which flow transversely of the electrodes and in the direction of movement of the running web in order to entrain the solid combustion products away from the gap or gaps. Reference may be had to the aforementioned German Offenlegungsschrift No. 2,934,044.
It has been found that the aforediscussed undertakings do not suffice to effect, and cannot guarantee, the removal of all solid combustion products which develop, for example, when a running web is subjected to the perforating action of pairs of electrodes and/or one or more beams of coherent radiation. More particularly, the aforediscussed stream or streams of air cannot prevent the accumulation of solid particles at the radiation discharging ends or outlets of orifices in nozzles or analogous devices which direct coherent radiation against a running paper web or the like. Such solid matter is likely to accumulate around the discharge ends of the nozzles and to gradually occlude the path for coherent radiation so that the perforating action of the apparatus is adversely influenced and the permeability of the treated web deviates from an optimum permeability. The accumulations of solid combustion products are particularly bothersome when the web which is to be perforated is in motion, i.e., when the perforations are to be made in a running web of cigarette paper, imitation cork or the like. In such apparatus, the solid combustion products have a component of movement in the direction of advancement of the running web and are highly likely to accumulate at the downstream sides of the radiation-directing devices, and more particularly at the downstream sides of the discharge ends of such devices to form nose-like projections rings or otherwise configurated accumulations which interfere with the propagation of beams of coherent radiation against the running web. The accumulations rapidly assume proportions which block substantial portions of orifices for the beams of coherent radiation so that, if the operation of the apparatus is to remain satisfactory, the radiation-directing devices must be inspected, cleaned or replaced at frequent intervals. This is a cumbersome and time-consuming procedure which is particularly undesirable in a modern filter tipping, filter rod making, cigarette rod making or an analogous mass-producing machine wherein each, even very short, interval of idleness entails extremely high losses in cigarettes, filter rod sections or like rod-shaped smokers' products or component parts of smokers' products. Furthermore, the apparatus which makes perforations in a running web of cigarette paper or the like, or in the wrappers of successive rod-shaped smokers' products, is not always readily accessible so that its inspection, cleaning and/or repair often necessitates at least partial dismantling of other constituents of a mass-producing filter tipping, filter rod making or analogous machine.